Better precision at lower cost is a major driving force in design and manufacturing. Traditionally, precision assemblies have used precision pins and holes for part alignments; but the demands of manufacturing processes have now pushed performance requirements beyond the approximately ten micron repeatability limits of such techniques. Next generation assemblies, such as, for example, machining fixtures, require low cost methods of assembly with consistently better than ten microns repeatability. The present invention is accordingly directed to a fundamentally new kinematic coupling, termed here a "quasi-kinematic" coupling, which meets the more stringent demands of these processes.
While certain types of prior kinematic couplings have been used to provide affordable submicron repeatability, their operation generally leaves gaps between the mated components, and they are therefore not well-suited for those types of precision assembly applications that require contact or sealing, such as in casting. This problem has been addressed in part by compliant kinematic couplings as described in U.S. Pat. No. 5,678,944, Flexural Mount Kinematic Coupling and Method, of common assignee Advanced Engineering Systems Operation and Products (AESOP) Inc. herewith. These types of couplings kinematically locate components and then allow translation parallel to the mating direction until contact is made between the desired surfaces. Though constituting a significant improvement, such couplings are not ideally suited for use in high volume manufacturing and assembly processes, due to the cost of manufacturing and assembling the flexural and kinematic components. Another limitation of these couplings resides in their inability to be arranged so that most of the resistance to error-causing loads is aligned in a common direction, while maintaining high stiffness in an orthogonal direction.
The present invention, on the other hand, as later more fully explained, overcomes such limitations by using conical shaped grooves with relieved sides which can direct a desired portion of their error resistance along a direction without seriously compromising the resistance to error in an orthogonal direction. Accomplishing this function in prior classical or flexural kinematic couplings is not achievable since their use of conventional straight V grooves leaves one degree of freedom and with very low stiffness.
In further U.S. Pat. No. 5,769,554, also of common assignee, an invention is described for use in sand casting and similar applications which incorporates kinematic elements into parts of the mold in a manner that admirably solves this problem, though only for low precision or sand mold assemblies and the like. The use of this coupling in large scale assembly and locating applications is, however, somewhat limited due to the fact that the kinematic elements must be pre-formed into the components. This technique, therefore, is not well suited for coupling situations requiring precision assemblies where machining of the mating surfaces is required, more specifically, in high precision assembly activities where the mating of the components is dependent upon the depth and size of the kinematic elements (i.e. grooves.) For such higher precision assemblies, this geometric relationship is sensitive enough that the capability of net shape manufacturing processes is insufficient to hold the relation between the kinematic features and the mating surface. While this problem may be addressed by machining the contact surfaces of the mated components, this would destroy the geometric relationship initially imparted to the components by the net shape process, nullifying the advantage of pre-formed elements.
In the absence of the ability to form, as, for example, by casting these kinematic features, they must be machined. Machining straight grooves into components requires translation motion in a minimum of two directions; depth perpendicular to the mating surface and translation in a direction contained in the plane defined by the contact surface. In comparison, the present invention, through using the principle of said patents, also introduces a novel way to form quasi-kinematic elements during a simple plunge operation using a rotating form tool, further providing a low cost method to manufacture these elements while simultaneously machining other features into the mated components.